Subsea Intervention Riser System

ABSTRACT

The invention comprises a multi-component system for subsea intervention. The system comprises a lower riser component which is held vertical by a buoyance element and an upper riser system. The upper riser system is a continuous, enjoined conduit with sufficient flexibility to absorb the motion of the deployment vessel without adversely affecting the function of the intervention system.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

REFERENCE TO A COMPACT DISK APPENDIX

Not Applicable.

TECHNICAL FIELD

The invention relates to a riser system for accessing and servicing sub-sea oil and gas wells and subsea equipment installations. The riser system may be used to access an existing well to carryout intervention operations or for interventions associated with other subsea installations and equipment such as subsea Xmas trees/well heads, manifolds, access points, pipelines, flowlines and umbilicals. Such access is required, for example, to take further measurements of the reservoir or to make various maintenance, inspection, and repair operations.

The invention provides a technique to enable subsea well, installation and flowline intervention using electric braided wireline, slick wireline, coiled tubing and numerous intervention tools required for such intervention. This invention allows vessels and rigs to quickly and efficiently access subsea wells, installations and flowlines.

BACKGROUND OF THE INVENTION

Subsea wells and fields are being developed in order to produce hydrocarbon based fluids from subsea environments. In order to develop such fields and wells, it is necessary to drill subsea well and install equipment on the seabed to enable production and fluid movement. During the production life of a subsea oil and gas field, there is a compelling case to perform interventions in order to maintain optimal production levels of desired fluids. Following equipment installation, subsea wells and seabed equipment installations periodically require maintenance, repair, inspection, further equipment additions, modification and development making it necessary to perform service related intervention work. In fields where access to wells can be performed from surface, multiple interventions are normally made to sustain optimal hydrocarbon production. For subsea wells and in particular where water depths become increased, the cost of performing simple or basic interventions become extremely high and also have significant associated potential risk.

In order to perform subsea intervention related service work, it is necessary to overcome several technical and operational hurdles. The industry would normally perform subsea well intervention using a drilling rig or similar heavy intervention vessel. Such intervention operations are very costly to mobilize and take several days to mobilize and demobilize for intervention operations. The industry has therefore pursued several alternate techniques for subsea well intervention work, mainly in shallow water depths with very special subsea intervention equipment including open water braided electric wireline, slick wireline, coiled tubing, lubricators, heave compensating cranes and pressure containing equipment. Such operations are normally also supported by remotely operated vehicles and divers.

BRIEF SUMMARY OF THE INVENTION

The dual riser system will consist of two main elements, a lower and a surface riser systems. The lower riser system will be connected to the well, equipment installation, pipes, other risers or flow line at the seabed level. At the top of the lower riser system, buoyancy will be fitted to preferably maintain the lower riser system in tension and thus in a near vertical orientation at some intermediate depth below the splash zone of the sea, typically from 100 m to about 300m, and with due consideration for depth allowance required to permit the surface riser system to absorb the vessel motion without damaging or impeding the operation of the intervention systems. Whilst it will be preferable to utilize a riser tube of un-jointed flexible unbonded composite pipe which could be positively buoyant and will preferably be complex bore, single bore steel, titanium or other composite material riser could also be utilized. Having positive buoyancy on the fully deployed lower riser system will help to keep riser under tension and near vertical. The internal bores of the riser systems will be made from composites or extrusions and will maintain position within the riser systems using spacers allowing interventions systems such as coiled tubing, wireline, slickline to move efficiently inside the riser system. The buoyancy provided on the lower riser system will incorporate a remotely operated vehicle (ROV) operable connector system that will allow the surface riser system to connect to the buoy and subsequently to the lower riser system. To assist in this task the buoy will be fitted with a ROV alignment system to ensure efficient connection process.

The surface riser system will also comprise preferably of riser tube fabricated from flexible unbonded continuous un-jointed composite pipe which would be positively buoyant and will preferably be complex bore. Single bore steel, titanium or other composite material riser could also be utilized. The bores in the riser system will allow for the deployment and free movement of fluids, coiled tubing, wireline or slickline within the riser system. The primary purpose of the surface riser system will be to absorb vessel motion without damaging or impeding the operation of the intervention systems. The surface riser system will be deployed with additional over length to create a sag bend to absorb vessel motion and thus avoid the high cost to have heave compensation incorporated in the deployment of surface intervention hardware. Access to the surface riser system will be vertical. The surface riser system can be disconnected from the riser in any abandonment situation e.g. for reasons of weather, drive off. The surface riser system preferably will also incorporate a disconnect system which will include sealing, disconnecting and cutting capability.

The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawing, in which:

FIG. 1 is an elevation view of a two-component riser system of the invention connected in a typical well intervention configuration;

FIG. 2 is a is an elevation view of a two-component riser system of the invention with an alternate intervention system for flow line intervention;

FIG. 3 is a is an elevation view of a two-component riser system of the invention intervening on a flow line or other subsea equipment installation;

FIG. 4 is a cross-section of a two-component riser system;

FIG. 5 is a cross-section of a riser system with complex bore;

FIG. 6 is a cross-section of a riser system with complex bore and external conduit.

DETAILED DESCRIPTION OF THE INVENTION

The invention allows for connection to any number of subsea installations to include Xmas trees, wellheads, manifolds, access points, pipelines, flow lines, umbilicals and resins to a subsea intervention vessel, rig or other type of craft. The invention enables subsea well, installation, pipeline and flow line invention utilizing a variety of equipment including, but not limited to electric braided wire line, slick electric wire line, coiled tubing and other intervention tools. The intervention tools may be remotely powered, subpowered or unpowered.

The riser system of the invention allows vessels and rigs to quickly and efficiently access subsea wells, installations and flow lines. Typical vessels that can deploy the system include open water light weight intervention vessels, light weight construction vessels, large construction and intervention vessels and rigs. The light nature of un-jointed flexible unbonded composite pipe enables the use of light weight vessels. The riser system can be deployed from a number of locations on the vessel to include the stern, side or through a moon pool.

Referring to FIG. 1, the riser system of the invention is deployed from a surface vessel 101 to access a subsea wellhead by the connection of the lower riser component 103 and the upper riser component 104. The riser system may be deployed through a moon pool 105 located in the center of the vessel 101 or it may be deployed from the stern or other locations on the vessel.

The lower riser component 103 is connected to the well head using standard connection methods. As shown in FIG. 1, the lower component 103 is connected to the wellhead 106 and includes above through a Blow Out Preventer (BOP) 107 and a Xmas tree 108. A coiled tubing BOP 109, a subsea lubricator 110 and an emergency disconnect system 111 complete the connection. A pressure activated sealing system (not shown) may also be used at the lower end of the lower riser component.

The lower riser component 103 is connected at its upper end to a Buoyancy element 112 which maintains tension on the lower component 103, keeping it in a vertical orientation. The buoyance element 112 is attached to the lower element such that it is below the splash zone of the sea and at a sufficient distance from the surface to permit the upper riser component 104 to absorb the vessel motion without damaging or impeding the operation of the system.

The lower riser component 103 may be a single or complex bore conduit fabricated from steel, titanium or composite materials. In one embodiment, the lower riser is fabricated from a flexible un-jointed unbonded composite material such as that described in U.S. Pat. No. 6,491,779, the teachings of which are hereby incorporated by reference.

The upper riser component 104 is connected to the lower component 103 by means of a riser disconnect package 113 and a swivel 114. A second buoyance element 115 is connected to the upper riser component 104 to provide buoyancy to the upper riser component. The second buoyance element helps define the desired curvature of the upper riser component and the desired shape to facilitate natural heave compensation. A slip joint or motion compensating system may also be used to compensate for the motion of the surface vessel.

As with the lower riser component, the upper riser component may comprise a pressure activated sealing system located at the lower end of the upper riser component.

The upper riser component is deployed such that there is excess length creating a sag band 116 allows the upper riser component to absorb the motion of the vessel.

To allow the upper riser to absorb the motion of the vessel, the upper riser component should be flexible so that the upper component can bend but in the sag bend without adversely affecting the function of the riser assembly. A variety of materials can be used to fabricate the upper riser component including steel, titanium, and composite materials. In one embodiment, the upper riser component is constructed of an un-jointed unbonded composite pipe such as that disclosed in U.S. Pat. No. 6,491,779, the teachings of which are hereby incorporated by reference. The riser is formed from a un-jointed continuous pipe.

The connection of the lower riser component 103 to the wellhead 106 and the upper riser component are accomplished by means of a remotely operated vehicle (ROV) 117. To facilitate the use of a ROV, the first buoyance element 112 is fitting a ROV alignment system to insure an efficient connection.

The upper riser component and the lower riser component may incorporate monitoring systems such as fiber optic monitoring systems. The monitoring systems can be integral to the riser component or mounted externally. The monitoring systems allow the user to monitor the riser system for shape, stress, fatigue, pressure and temperature.

The riser system can be either a single bore or a complex bore. By complex bore, it is meant a riser having two or more bores within the riser system. The bores may be of different sizes and used for different purposes such as fluid conduit, fluid return conduit, umbilical conduit, and tool and conveyance system conduit. The upper and lower riser components may be lined or unlined.

The riser system can remain attached to the subsea well installation or flow line. This allows rapid return access should suspension or disconnection be required.

The flexible nature of the unjointed riser system permits efficient deployment of the riser system and facilitates movement and shape adjustment enabling easy tool or assembly deployment. The vertical nature of the lower riser component permits gravity assistance from tool for assembly deployment.

Another embodiment of the invention is shown in FIG. 2. In this case, the riser system is used to access a subsea flow line or pipeline 201. In this embodiment, the lower riser component 202 engages the pipeline 201 through a subsea manifold 203 or similar installation. Again, a BOP 204 is in place between the manifold 203 and the lower riser 202. An emergency disconnect 205 optimal components such as a lubricator 206 and a coil tubing BOP and stripper 207 may also be deployed between the manifold 203 and the lower riser 202.

FIG. 3 shows an alternate embodiment where the riser system is again attached to a flow line or pipeline. In this embodiment, the lower riser 301 connects with a BOP 302 which in turn is connected to a pipeline elbow 303. The elbow 303 engages a subsea connection tool system 304 which, in turn is connected to the pipeline 305. As with the other embodiments, an emergency disconnect system 306 is placed between the riser 301 and the BOP. An optimal lubricator 307 and coiled tubing BOP 308 is also shown.

As discussed above, the bore of the riser can be a single bore or a complex bore with the bores serving different functions. FIG. 4 is an illustration of a single bore riser of the invention. In this example, the riser has a simple outer layer 401 and a second smaller layer 402.

In this example, an external conduit 403 is also provided. The external conduit can be used in a variety of ways to include deployment of a fiber optic monitoring system like that discussed above.

FIG. 5 shows an example of a complex bore for an intervention riser system. In this case, the riser has an outer layer 501 and one inner layer 502. Within the inner layer, there are separate conduits 502, 503 and 504. The system may also have further conduits.

In this example, the conduits comprise a conduit fitted for a control power or communications umbilical 503, a conduit for coiled tubing 504 and a conduit for wire line or slick line 505. As discussed above, a variety of different conduits can be used with the riser. The illustrative conduits are merely exemplary and do not emit the range of possible conduits.

FIG. 6 is a cross section of yet another embodiment of the invention. In this embodiment, a complex bore 601 has internal conduits 602, 603 and 604. In addition, the riser system has an external conduit 605 fitted to the riser system.

Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 

1. A subsea intervention system comprising: (a) a lower riser component; (b) a first buoyancy element attached to the upper end of said lower riser component; (c) an upper riser component extending between the upper end of said lower riser component and a surface vessel, said upper riser component having sufficient flexibility to absorb the motion of said surface vessel without adversely affecting the operation of said intervention system; (d) a second buoyancy element attached to said upper riser system, wherein said upper riser component comprises continuous un-jointed, unbonded composite pipe.
 2. The intervention system of claim 1 wherein said lower and upper user components comprise multi bore risers.
 3. The intervention system of claim 1 further comprising a disconnect system between said upper and lower riser components.
 4. The intervention system of claim 1 wherein said lower riser component is connected to a Xmas tree.
 5. The intervention system of claim 4 further comprising a Blowout Preventer placed between said lower riser component and said Xmas tree.
 6. The intervention system of claim 1 further comprising an external conduit mounted to said upper and lower riser components.
 7. The intervention system of claim 1 wherein the upper and lower riser components are lined.
 8. The intervention system of claim 1 further comprising a pressure activated sealing system at the bottom of the upper riser component.
 9. The intervention system of claim 1 further comprising a motion compensation system located between the upper and lower riser components.
 10. A subsea intervention system comprising: (a) a lower riser component; (b) an upper riser component extending between said lower riser component and a surface vessel, said upper riser component comprising continuous, un-jointed, unbonded composite pipe;
 11. The intervention system of claim 10 wherein the upper riser component has sufficient flexibility to absorb the motion of said surface vessel without adversely affecting the operation of said intervention system.
 12. The intervention system of claim 10 wherein the said upper and lower riser components comprise two or more bores.
 13. The intervention system of claim 10 further comprising a disconnect system located between said upper and lower riser components.
 14. The intervention system of claim 10 further comprising a disconnect system between said upper and lower riser components.
 15. The intervention system of claim 10 wherein said lower riser component is connected to a Xmas tree.
 16. The intervention system of claim 15 further comprising a Blowout Preventer placed between said lower riser component and said Xmas tree.
 17. The intervention system of claim 10 further comprising an external conduit mounted to said upper and lower riser components.
 18. The intervention system of claim 10 wherein the upper and lower riser components are lined.
 19. The intervention system of claim 10 further comprising a pressure activated sealing system at the bottom of the upper riser component.
 20. The intervention system of claim 10 further comprising a motion compensation system located between the upper and lower riser components.
 21. The intervention system of claim 10 where in the lower riser component comprises continuous/un-jointed unbonded composite pipe. 